More specifically, this invention relates to electrical resistance welding clamps, of the general type including a rigid frame, associated with a support such as a rigid foot or a manipulating robot, a so-called articulation subassembly, associated with the frame and itself comprising a first so-called stationary arm, to which a first so-called stationary end is secured, a second so-called mobile arm, to which a second so-called mobile end is secured, and a main or welding actuator, bearing against said stationary arm so as to move the mobile arm (and end) with respect to the stationary arm (and end), according to a first degree of freedom, in translation or rotation, so as to close or open the clamp, in order, respectively, to grip a sheet metal assembly to be assembled between the stationary and mobile arms (and ends) (brought together by the actuator) or to release the sheet metal assembly, by separating the arms (and ends) from one another by the actuator.
Below, is described the principle of a welding clamp without the balancing/relief function as described in the French patent application 06 04384 filed in the name of the ARO company.
However, the problem remains identical in any type of clamp serving to grip a sheet metal assembly and integrating or not integrating an additional degree of freedom between the frame and the stationary arm so as to perform a balancing and relief operation.
In the electrical resistance welding clamps of the prior art, depending on the work to be performed, two kinematics are possible for the mobile arm and end:                the first degree of freedom is a translation of the mobile arm and end with respect to the stationary arm holding the stationary end, by linear guidance provided by the welding actuator, which is a linear actuator of any suitable known type, i.e. hydraulic, pneumatic, mechanical or electric, which directly moves the mobile arm and end, in which the clamp is then said to be a C- or J-clamp, as shown in the appended FIG. 1, or        the first degree of freedom is a rotation of the mobile arm and end, around a pin on the frame, with respect to the stationary arm holding the stationary end, in which the clamps are then said to be X- or scissor-clamps, and in which the welding actuator can be a linear actuator, of the cylinder type, either mounted pivotably by its body on the frame (appended FIG. 2a) around a pin parallel to the pivot pin of the mobile arm and end, or attached rigidly to this same frame (appended FIG. 2b), in which a suitable mechanical connection with two degrees of freedom then enables the rod of the cylinder moving linearly to follow the pivoting movements of the mobile arm around the pivot pin. The pivot force of the mobile arm and end is transmitted from the actuator to the mobile arm by a lever, to which the mobile arm is secured, pivoting around the pivot pin, and on which the end of the rod of the actuator pivots, as shown in the appended FIGS. 2a and 2b.         
In FIGS. 1 to 11, the same references designate identical or equivalent components in the C- and X-clamps.
To ensure the electric spot welding of a sheet metal assembly 1, the C-clamp of the prior art according to FIG. 1, like that of the invention according to FIGS. 3, 4 and 5, includes primarily a stationary end electrode 2 mounted at the end of a stationary arm 3 secured to a support frame 10 of a welding actuator 4, for example of the pneumatic cylinder type, of which the piston 6 and the rod 7 are secured in movement to a mobile arm 8, in the extension of the rod 7, and of which the free end supports a mobile end electrode 9. These components form a so-called articulation subassembly 12 rigidly connected to a manipulating robot or a rigid foot, 30, called a support element.
Similarly, in the X-clamp of the prior art according to FIG. 2a, like that of the invention according to FIGS. 6, 7 and 8, the stationary end electrode 2 and the stationary arm 3 are secured to a frame 10 in which a pivot pin 13 is mounted, around which a rigid lever 14 supporting the mobile arm 8 and the mobile end electrode 9 pivots, in which the welding actuator 4, also linear, pivots by its body 5 on the frame 10 around a pin 15 parallel to pin 13, while the free end of the rod 7 of the actuator 4 actuates the lever 14, on which the rod 7 pivots around a pin 16 also parallel to pin 13 and connected to the lever arm 14, so as to control the pivoting of the arm 8 and electrode 9 mobile in rotation around the pin 13 with respect to the arm 3 and end 2 stationary with respect to the frame 10 of the tool. As for the C-clamp described above, these components form a so-called articulation subassembly 12 rigidly connected to a manipulating robot or a rigid foot 30, called a support element.
In a variant of the X-clamp according to the prior art and according to the invention, and as shown, respectively, in FIGS. 2b and 10, the rotation of the rigid lever 14 supporting the mobile arm 8 and the mobile end 9 around the pivot pin 13 is controlled by an always-linear welding actuator 4, rigidly attached by its body 5 and the attachments 4′, such as screws, to the frame 10. A suitable mechanical connection 17 with two degrees of freedom, such as, for example, a connecting link system 18 mounted at the free end of the rod 7 and in rotation on said rod 7 by a first pin 19 parallel to pin 13 and by a second pin 16 also parallel to pin 13, on the lever arm 14, so as to control the pivoting of the arm 8 and end 9 mobile in rotation around the pin 13 with respect to the arm 3 and end 2 stationary with respect to the frame 10 of the tool, during translation movements of the rod 7 of the welding actuator 4. As for the 2 C- and X-clamp variants described above, these components form a so-called articulation subassembly 12, rigidly connected to a manipulating robot or a rigid foot, 30, called a support element.
The mechanical connection between the articulation subassembly 12 and the support element 30 can be produced:
either directly as in FIGS. 2a and 2b, 
or by means of one or more components forming a rigid assembly and which may or may not be part of the tool. FIG. 1 shows the possibility of a connection by means of at least one other rigid component 20 which may or may not be part of the clamp.
This component 20 can be, for example, in a non-limiting manner, a welding transformer when it is integrated in the clamp, a tool changer or a balancing cassette as described in the French patent application 06 04384 filed in the name of the ARO company.
According to the prior art, the design of welding clamps provides great diversity to frames, depending on the articulation subassembly used. However, no design makes it possible, for a line of clamps including C- and X-clamps, to use a frame with a similar design making it possible to obtain, according to different size and/or kinematics models (C- or X-clamp), synergy in the supply and management of said component.
An objective of the invention is to overcome this disadvantage, and to provide means for producing a clamp and a line of clamps for gripping sheet metal, which are more suitable for the various requirements of the field than similar clamps and lines of clamps of the prior art.